Urinary tumour necrosis factor- excretion independently correlates with clinical markers of glomerular and tubulointerstitial injury in type 2 diabetic patients

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BACKGROUND: Inflammation is a potential factor in the development and progression of diabetic nephropathy. The aim of this study was to analyse the relationship between the pro-inflammatory cytokine tumour necrosis factor-alpha (TNFalpha) and clinical markers of glomerular and tubulointerstitial damage [urinary albumin excretion (UAE) and urinary N-acetyl-beta-glucosaminidase (UNAG), respectively] in a large group of type 2 diabetic patients. METHODS: A total of 160 diabetic patients and 32 healthy controls were included in the study. High-sensitive C-reactive protein (hs-CRP) as well as serum and urinary levels of TNFalpha were measured. UAE and UNAG were determined by 24-h urine collection. RESULTS: Serum hs-CRP and TNFalpha were significantly higher in diabetic than in control subjects, as well as UAE and UNAG. Diabetic patients had increased urinary TNFalpha compared to non-diabetics [14.5 (2-29) vs 4 (0.8-12), P < 0.001]. Serum hs-CRP and TNFalpha in diabetics with increased UAE were elevated compared to diabetics having normoalbuminuria. Urinary TNFalpha was also higher in diabetic subjects with micro- or macroalbuminuria than in patients with normal UAE [10.5 (4-20) and 18 (9-29) vs 7 (2-18) pg/mg, P < 0.0001, respectively]. Multiple regression analysis showed that urinary TNFalpha (P < 0.0001), hs-CRP (P < 0.0001), serum TNFalpha (P < 0.01) and HbA1c (P < 0.05) were independent of and significantly associated with UAE, whereas duration of diabetes (P < 0.001), urinary TNFalpha (P < 0.01), HbA1c (P = 0.01), hs-CRP (P < 0.05) and serum creatinine (P < 0.05) were associated with UNAG. CONCLUSIONS: In patients with type 2 diabetes, urinary TNFalpha excretion is elevated and correlates with severity of renal disease in terms of both glomerular and tubulointerstitial damage, suggesting a significant role for TNFalpha in the pathogenesis and progression of renal injury in diabetes mellitus.